Embodiments of the present disclosure generally relate to neurostimulation (NS) systems, and more particularly to systems and methods for recording evoked potentials resulting from NS for closed loop spinal cord stimulation.
NS systems are devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders via one or more electrodes. For example, SCS has been used to treat chronic and intractable pain. Another example is deep brain stimulation, which has been used to treat movement disorders such as Parkinson's disease and affective disorders such as depression. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of electrical pulses depolarize neurons and generate propagating action potentials into certain regions or areas of nerve tissue. The propagating action potentials effectively mask certain types of physiological neural activity, increase the production of neurotransmitters, or the like. For example, applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions. Inducing this artificial sensation replaces the feeling of pain in the body areas effectively masking the transmission of non-acute pain sensations to the brain.
During stimulation by the NS systems, evoked potentials are emitted from the stimulated nerve tissue. The evoked potential signals may be generated by neuronal transmembrane currents of neurons activated following or in response to the NS. The simultaneous activation of multiple neurons generates a signal of sufficient amplitude for recording. The evoked potential signals propagate within the population of sensory nerve fibers through subsequent orthodromic or antidromic propagation from the excitation site. It has been proposed that the NS system may measure the evoked potential for a feedback mechanism to adjust the NS.
However, the evoked potential signals are measured proximate to the source of the NS, specifically, the electrodes of the NS system near the dorsal column. Due to the proximity, the evoked potential signal includes stimulation artifacts corresponding to the NS emitted by the electrodes. Further, the evoked potential signal measured at the dorsal column primarily corresponds to the excitation of the sensory Aβ fibers, since the Aδ and C fibers indicating pain travel in a different pathway located away from the dorsal column. Moreover, the thickness of the cerebrospinal fluid around the dorsal column reduces the evoked potential signal. A need exists to overcome the shortcomings of traditional recording locations of the evoked potential signal.